Sleep and wakefulness are natural behavioural phenomena present across the species and across age. During sleep, the living being takes rest, recuperates from lost energy and feels afresh. Lack of sleep or lack of adequate sleep due to any reason, for instance, any disease, results in mental as well as physical fatigue.
Sleep has been classified into slow sleep, deep sleep and rapid eye movement (REM) sleep. During slow sleep, the electroencephalogram (EEG), follows synchronized pattern while during REM sleep, the EEG is desynchronized. The REM sleep is unique in the sense that some of the signs during this phase are similar to those during wakefulness while others are similar to those during sleep. Irregular heart beat rate and respiration, periods of involuntary muscle jerks and movements and higher threshold for arousal further characterize the REM sleep. Periods of desynchronized sleep occupy about 20% of the sleeping time and dreams usually occur during this phase of sleep.
Sleep including REM sleep, can be assessed subjectively and behaviourally. However, in order to avoid subjectivity and for adequate quantification, continuous electrophysiological recordings of electroencephalogram (EEG), electrooculogram (EOG) and electromyogram (EMG) are done. One of the disadvantages of this approach is the need for fixing electrodes on the skull for recording EEG, in the muscles of the neck and eye for recording EMG and EOG, respectively. While it may be argued that these procedures are non-invasive, for recording in the humans, they suffer from a major disadvantage of requiring the subject to spend the night in the sleep lab. Even if the subject does not wish to spend the night in a sleep lab, an electrophysiological recording unit has to be moved to the bedside of the patient. Another major disadvantage is that the recording has to be carried out over the night and requires the presence of a trained nurse throughout. A huge quantity of paper recording—of the order of one third of a mile long—must be scored and evaluated by trained personnel. To avoid such drawbacks, prior art has attempted to conduct analysis with the help of computers with relevant software. Nevertheless, the overall elctrophysiological process of recording is quite cumbersome, time consuming and expensive and not readily adaptable to ambulatory or home based monitoring.
Behaviourally, REM sleep loss is reported to cause increased irritability, excitability, sexuality, loss of concentration and coordination, reduced memory consolidation and brain maturity etc. A significant number of early morning road and industry related accidents are attributed to sleep loss including REM sleep loss. Such loss may even lead to social misbehaviour including in work place leading to reduced efficiency and productivity. It has been reported that at any given time, about one third of the adult population is likely to complain of insomnia, while a small proportion complain of being excessively sleepy. The number of patients with sleep related problems have increased dramatically over the years and continues to increase.
Although polysomnography has an important role to play in this regard, its availability and application are very limited. Even a large sleep disorders center can only cater to the need of a relatively small number of patients as compared to the number of patients who are required to be tested. Also, polysomnography does not address all relevant aspects of a disorder. Hence, there is an urgent need to develop a simpler and quicker testing method to evaluate REM sleep loss/disturbance.